# Team:Dundee/Project/DetectionComparison

### From 2013.igem.org

**Detection Comparison**

## Introduction

The direct method for detecting microcystin in water samples is high performance liquid chromatography (HPLC). This long process takes approximately 24 hours and is expensive due to the equipment required. For this reason, the current method for regulating toxic microcystin levels in Scotland uses the indirect approach of cyanobacterial cell counts. Using our biological detector we hope to reduce the time and cost of microcystin detection.

We examined the effect that a 24 hr detection time can have on the numbers of cyanobacteria and microcystin found in the water body. This then allowed us to determine whether faster detection methods are necessary.

## Theory

- t = 0 is the time water samples are taken
- b
_{0}is the initial number of cyanobacteria at t=0 - t is the time in hours after the water samples are taken
- cyanobacteria undergo binary fission every hour
- cyanobacteria growth is uninhibited
- each cyanobacteria releases N microcystin molecules

We arrive at these equations:

where b(t) is the number of cyanobacteria at time t and MC(t) the number of microcystin molecules.

Since HPLC results are obtained 24 hours after the water samples are taken i.e. t=24, we compared this against our aim of a 1 hour detection time t=1 by evaluating equation (2).

Dividing MC(24) by MC(1) we recover an expression for MC(24) in terms of MC(1).

## Results

Correspondingly, after 24 hours there can be up to 8.4 million times more microcystin molecules present than there is after 1 hour. Putting this ratio into perspective, this is the same as the height of the Empire State Building being compared with the combined height of 7

*E. coli*.

Therefore, in the time period between collection of samples and obtaining results there can be vast increases in the concentration of microcystin present in the water body. This emphasises that HPLC is an unsuitable method for toxin detection and that a 1 hour detection period is much more efficient.

Generally we can conclude that faster detection methods are necessary and our biological detector is worthwhile pursuing if we can reduce this detection time.